The invention relates to a workpiece handling device in a machine tool, particularly an internal broaching machine, the said handling device comprising a workpiece feed device which is adapted to perform a reciprocating movement and by which one or more workpieces are brought from a workpiece transfer device, adapted to perform a reciprocating movement perpendicularly to the feed device, to one or more machining stations spaced the same distance apart, and thence returned to the transfer device.
A handling device of this kind, which is provided in an internal broaching machine, and which is primarily constructed as a workpiece indexing device, is known from German Offenlegungsschrift No. 1,752,719. In this known feed device, workpieces are fed one after the other to different broaching stations after indexing by a determined angle in each case.
The invention is based on the use of workpiece holders, in which the workpieces themselves are held, for the purpose of fixing a determined spatial position of the workpiece. The use of workpiece holders of this kind is already known in various fields of technology, although not in the field of broaching, in which fields workpieces are held in the workpiece holders and are fed one after the other to various machining stations; the workpiece itself does not have to be set up anew each time and does not change its position relative to the workpiece holder, so that only the latter has to be adjusted, which is very much simpler.
When workpiece holders of this kind are used the problem arises of bringing the workpiece holders back each time to the starting point, where they are filled with a further workpiece to be machined.
The problem underlying the invention therefore resides in so developing a feed device of the kind first described above that without any noteworthy additional expense for construction and without additional working steps the workpiece holders are automatically brought back to the starting point after the machining of the workpieces contained in them, and are there loaded with further workpieces to be machined.
According to the invention this problem is solved by providing in the feed device two pairs of drivers for each individual machining station, these drivers lying in each case against two surfaces of workpiece holders holding the workpieces, which surfaces lie opposite one another and perpendicularly to the direction of movement of the feed device; that the center-to-center distance of the transfer device from the machining station or stations is equal to the center-to-center distance of the pairs of drivers of the feed device. Pairs of drivers are disposed in the transfer device which are spaced apart to correspond to the machining stations and the number of which is at least one greater than but at most twice as great as the number of machining stations, and which bear in each case against two workpiece holder surfaces lying opposite one another and parallel to the direction of movement of the feed device.
These measures ensure that the workpiece holders rotate in a closed cycle and that in each case they can be loaded with unmachined workpieces before they move to the machining station that is to say particularly a broaching station, while after the machining they can be freed of the machined workpieces. No additional expense for control or drive means is necessary, since the feed device and the transfer device only move in each case to-and-fro between two end positions. A preferred field of application comprises vertical internal broaching machines. The device is used for example for broaching profiled bushes such as are used in industry for connecting shafts the lengths of which are variable. In principle the measures of the invention may however also be applied to other machine tools, such as for example honing machines, drilling and thread cutting machines, milling machines, and the like, in which either a workpiece is subjected in succession to a number of machining operations at different machining stations lying one behind the other, or, because of a very irregular shape of the workpiece, a workpiece holder adapted to this irregular shape is necessary for its machining. In addition, the invention may be applied to processing machines, for example in the packing field, when for example a container (for example a plastic bag) contained in a holder is filled, closed, and marked in a plurality of stations and thereupon the empty holder has to be returned to its starting position.
If it is not necessary for the cross section of the workpiece which is to be machined to be in a determined position in relation to the outer contour of the workpiece, the workpiece holders can in principle be given any external shape. If on the other hand the internal profile of the surfaces of the workpiece which are to be machined have a clearly defined position in relation to the external contour of the workpiece, guide surfaces must be provided in the workpiece holder. These guide surfaces may for example be in the form of grooves in the peripheral wall or end of the workpiece holders. It is however expedient for the surfaces of the workpiece holder which lie opposite one another to be in each case on the form of parallel surfaces, that is to say for the workpiece holder to have approximately the shape of a right parallelpiped.
It is advantageous for the transfer device to be in the form of a plate-shaped sliding element which on its surface carries the workpiece holders and which is provided with upwardly projecting drivers. In this case the workpiece holders, with or without workpieces, stand on this sliding element and are moved by it parallel to the plane of the machining stations and at right angles to the direction of movement of the transfer device.
In addition, it is advantageous for the feed device to be in the form of a carriage disposed above the transfer device and provided with downwardly projecting drivers. In this case there must naturally be a sufficient distance between the sliding elements in the carriage, in order to leave room for the workpiece holders between them. In principle it would also be possible for the sliding element of the transfer device to be disposed at the top and the carriage of the feed device at the bottom; this would however entail the disadvantage that the carriage carrying the workpiece holders together with the workpiece would have to transmit the broaching forces to the machine bed during the broaching operation.
Particularly simple movement of the workpiece holders from the sliding element of the transfer device to the machining stations and back, and from the sliding element to a position remote from the machining stations and back again, is achieved if on both sides of the sliding elements there are provided support plates the horizontal surfaces of which are in line with the likewise horizontal surface of the sliding element, the support plate facing the machining station or stations extending as far as the machining station or stations. During the broaching operation the workpiece holders can stand for example on the support plate, which consists of one or more parts and which takes direct the vertical broaching forces. Absolutely accurate lateral positioning of the workpiece holders not situated on the transfer device is ensured if guide bars are provided on the support plate which extend parallel to the direction of movement of the feed device and laterally guide the holders on the operation of the feed device.
The lateral position of the workpiece holders in the direction of movement of the transfer device is thereby fixed, particularly at the machining station, while the exact position on the direction of movement of the feed device is ensured by the drivers mounted on the latter.
It is expedient for the drivers to be in the form of plates, in which case they are narrower than the parallel surfaces of the workpiece holders against which they bear, and the drivers of the transfer device do not overlap vertically the drivers of the feed device. At least one of these measures is necessary in order to make it impossible for the drivers of the transfer device to collide with the drivers of the feed device during the individual movement steps.